1. Field of the Invention
The present invention relates to a dental filling instrument and an attachment therefor, and particularly relates to a dental filling instrument used to inject a filler into a tooth cavity in dental treatment and an attachment that can be attached to the dental filling instrument.
2. Description of the Related Arts
Heretofore, various dental filling instruments for injecting a dental filler such as gutta-percha or resin into a tooth cavity (such as a root canal or a defective part of a tooth) have been proposed for dental treatment.
Japanese Examined Laid-Opened Patent Publication No. HEI 1-40621 (International Publication Number: WO82/03761, International Application Number: PCT/US81/00589), for example, discloses a syringe-type filling instrument having a push rod to be thrust forward to extrude a filler in a state softened by heating with a heater from the tip of a needle.
A gun-type filling instrument 2 as shown in FIG. 1 is designed to thrust forward a push rod 4 by means of a ratchet mechanism when a lever 3 is pulled, thereby extruding a filler in a state softened by heating with a heater 5 from a tip 7a of a needle 7.
Such conventional filling instruments, however, require application of a large force to the push rod or the lever to extrude the filler. It is therefore not easy to hold the filling instrument so as not to displace the needle tip from a filler-pouring position even when a larger force is applied to the push rod or lever with a finger. For this reason, the user of such a filling instrument is required to become skillful. If the filler is not sufficiently softened, a larger force is required to extrude the filler and, hence, it is difficult to perform the operation of delicately moving the needle tip position as the filler-pouring operation proceeds and the operation of extruding the filler at the same time. Further, at the same time with the operation of extruding the filler, the operator needs to lift the needle tip gradually while sensing a subtle pressure of raising the needle tip received from the filler injected. Thus, the conventional instruments require the operator to perform complicated operations while paying attention to many different points.
When a root canal 8 is to be filled with a filler 9 as shown in FIG. 2, filler 9a may overflow from an apical part Ba if the filler is extruded in an excessive amount or abruptly. It is pointed out that such an overflowed filler 9a leads to unsatisfactory convalescence; for example, filler 9a causes a pain when the patient is subjected to percussion or it takes a longer time for filler 9a to be completely absorbed.
If the filler is cooled during the extrusion thereof from the needle, it is possible that the filler cannot be filled closely into a tooth cavity or that the filler adheres to the needle and hence is withdrawn from the tooth cavity along with the needle when the needle is withdrawn from the tooth cavity after the injection of the filler.
In an operating method including an insertion of a solid filler into a root canal, a cut of the filler to a predetermined length and an injection of a softened filler, it is possible that the solid filler is cut by heating with a needle attached to a filling instrument. Such a cutting operation is difficult if the needle is cool.
A root canal filling method has been proposed which includes an insertion of a solid filler in the form of an elongate tapered stick such as a master point or an accessory point into an apical foramen to plug it and a cut off an unnecessary portion of the stick-shaped filler other than the tip portion plugging the apical foramen by instantaneously fusing the filler (for about one second) with a heated leading end of an attachment called “spreader”. There has been proposed another root canal filling method which uses an attachment called “plugger” to press a filler injected into a root canal against the root canal in order to fill the root canal with the filler air-tightly. When such a root canal filling method is used before or after the injection of a filler, an instrument used in one operation needs to be replaced by another to be used in another operation. Such an exchange makes the filling operation cumbersome. Further, if instruments used in respective operations are different in size, shape, weight or the like from each other, a feel or touch in one operation is different from that in another operation, making each operation more difficult.
Still another filling method uses different fillers for different parts of a root canal; for example, a filler of the low-temperature-melting type which melts at a low temperature is used in an apical part requiring tight sealing, while a common filler of the high-temperature-melting type which melts at a high temperature is used in a main root canal portion. In this case, provision of different filling instruments for respective fillers having different properties raises a problem of cost. Further, there is a need for adjusting and operating filling instruments respectively, resulting in a cumbersome and complex operation with low efficiency.